Actuator having a permanent magnet

ABSTRACT

A solenoid for use in a valve such as an exhaust gas recirculation valve for a motor vehicle. The solenoid includes a housing having a coil for generating a first magnetic field. An armature is slidably mounted in the housing. The solenoid further includes a permanent magnet having a second magnetic field, wherein the magnet is located adjacent the armature. In addition, a stator is affixed in the housing for cooperation with the armature and the magnet to form a third magnetic field.

CROSS REFERENCE TO RELATED APPLICATION AND PRIORITY CLAIM

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/373,382 (Attorney Docket No. 2002 P 06213 US) filedon Apr. 12, 2002 in the name of Gilles Delaire and Frederic Gagnon andentitled USE OF A MAGNET IN A LINEAR SOLENOID ACTUATOR, which isincorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates to evaporative emission control systemsfor internal combustion engines, and more particularly, to an actuatorhaving a permanent magnet for increasing armature force anddisplacement.

BACKGROUND OF THE INVENTION

[0003] Many motor vehicles utilize actuators such as solenoids tooperate several types of devices. This includes devices such as a fuelcell valve or an exhaust gas recirculation (EGR) valve used in an EGRsystem. In such systems, the EGR valve is controlled by a circuit inaccordance with various engine operating conditions to regulate theamount of engine exhaust gas that is recirculated back into the enginefor combustion. This serves to limit the combustion temperature andhence reduce the formation of oxides of nitrogen.

[0004] Solenoids typically utilize an electromagnet coil to generate amagnetic force which causes an armature to move along an axis. Thearmature may be part of a mechanism for operating a valve, such as anEGR valve. Referring to FIG. 1, an enlarged view of a first magneticflux density 10 located near portions of a lower stator 12, upper stator46, gap 36, first armature 14 and coil 16 of a conventional solenoid isshown. It is noted that the configuration shown is substantiallysymmetrical about an axis of the solenoid and that only one side of theaxis is shown for purposes of clarity. The lower stator 12 has afrusto-conical shape having a predetermined geometry and is separatedfrom the upper stator 46 by a gap 36. The shape of the lower stator 12along with the size of the gap 36 and other parameters are selected soas to optimize a flux path that forms a part of a magnetic circuit. Thisprovides a desired solenoid characteristic in that the armature force issubstantially constant with respect to armature displacement. Referringto FIG. 1, the magnetic flux density vectors are oriented in asubstantially clockwise configuration in a lower portion 18 of the firstarmature 14 adjacent to the lower stator 12. In addition, the magneticflux density vectors are relatively dispersed along an edge 20 of thelower portion 18. In this configuration, the magnetic flux density in anupper section 22 of the lower stator 12 ranges from approximately 1597to 2195 kiloGauss (kGauss).

[0005] It is desirable that solenoids used in motor vehicles provideincreased armature force and increased travel so as to improvecontrollability and increase flow. However, this would require largersolenoids and the amount of space available in current vehicle enginecompartments is limited.

SUMMARY OF THE INVENTION

[0006] A solenoid which includes a housing having a coil for generatinga first magnetic field. An armature is slidably mounted in the housing.The solenoid further includes a permanent magnet having a secondmagnetic field, wherein the magnet is located adjacent the armature. Inaddition, a stator is affixed in the housing for cooperation with thearmature and the magnet to form a third magnetic field.

[0007] The features of the invention believed to be novel are set forthwith particularity in the appended claims. The invention itself,however, both as to organization and method of operation, may be bestunderstood by reference to the following description taken inconjunction with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a view of a first magnetic flux density in aconventional solenoid.

[0009]FIG. 2 is a cross sectional view of a solenoid having a permanentmagnet in accordance with the present invention.

[0010]FIG. 3 is a view of a second magnetic flux density in accordancewith the present invention.

[0011]FIG. 4 depicts first and second curves which show force anddisplacement properties for a conventional solenoid and for a solenoidof the present invention, respectively.

DETAILED DESCRIPTION OF THE INVENTION

[0012] While this invention is susceptible of embodiment in manydifferent forms, there is shown in the drawings and will herein bedescribed in detail specific embodiments, with the understanding thatthe present disclosure is to be considered as an example of theprinciples of the invention and not intended to limit the invention tothe specific embodiments shown and described. In the description below,like reference numerals are used to describe the same, similar orcorresponding parts in the several views of FIGS. 1-4.

[0013] Referring to FIG. 2, a cross sectional view of an actuator suchas a solenoid 24 including a permanent magnet 26 in accordance with thepresent invention is shown. The solenoid 24 includes a housing 28 havingan internal passageway 30 which is in fluid communication with an outletport 32 and an inlet port 34. When the solenoid 24 is used in an exhaustgas recirculation (EGR) valve, the inlet port 34 is in fluidcommunication with engine exhaust gas and the outlet port 32 is in fluidcommunication with an engine induction system of an internal combustionengine. It is noted that the current invention may be used in othertypes of devices that use actuators, such as fuel cell valves.

[0014] The coil 16 is symmetrically disposed about a first axis 40 ofthe housing 28. The housing 28 includes a second armature 42 that isaffixed to a valve stem 44. A portion of the second armature 42 islocated within an upper stator 46 that is affixed to the housing. Theupper stator 46 is separated from the lower stator 12 by the gap 36. Thelower stator 12 is symmetric about the first axis 40 and is locatedadjacent the second armature 42. The lower stator 12 includes a firstbore 48 and a second bore 50 of reduced size that is bounded by an endwall 52. The lower stator 12 further includes an axially extending sidewall 54. A tapered wall 56 extends from the side wall 54 toward thefirst axis 40 and terminates at a tip surface 64 adjacent the magnet 26to form a substantially frusto-conical configuration.

[0015] The permanent magnet 26 includes top 60 and bottom 62 surfaces.The magnet 26 is substituted for a portion of the first armature 14 in aconventional solenoid such that the overall size of the second armature42 and magnet 26 is substantially equivalent to that of the firstarmature 14, resulting in a solenoid of substantially the same size. Themagnet 26 is positioned in the first bore 48 such that the top surface60 is adjacent the second armature 42 and substantially colinear withthe tip surface 64. As will be described, the magnet 26 is located sothat its magnetic field is added to the first magnetic field 10generated by coil 16. This results in a solenoid having a substantiallyhigher armature force within substantially the same solenoid volume.

[0016] The housing 28 further includes a spring 66 located in the first48 and second 50 bores between the bottom surface 62 of the magnet 26and the end wall 52. A bearing member 68 is affixed within the housingbetween the end wall 52 and the passageway 30. The stem 44 extendsthrough the magnet 26, spring 66, end wall 52, bearing member 68 andinto the passageway 30. A bottom end 69 of the stem 44 includes a valvehead 70 shaped for cooperation with a valve seat 72 formed in the inletport 34.

[0017] The bearing 68 enables movement of stem 44 along the first axis40. This enables movement of the valve head 70 between open and closedpositions. In the open position, the valve head 70 is spaced downwardfrom the seat 72 to enable fluid communication between the inlet 34 andoutlet 32 ports. In the closed position, the valve head 70 contacts theseat 72 to thus close the inlet port 34 as shown in FIG. 2. The spring66 is biased against the bottom surface 62 of the magnet 26 to urge themagnet 26 and thus the valve head 70 to the closed position. Uponenergization of the coil 16, a magnetic field is generated which issufficient to overcome spring bias to cause downward movement of thesecond armature 42 and place the valve head 70 in the open position. Thehousing 28 also includes a connector 74 which serves to transmitelectrical power from a power source to the coil 16 for forming thefirst magnetic field 10.

[0018] Referring to FIG. 3, an enlarged view of balloon section 76 ofFIG. 2 is shown. FIG. 3 depicts a second magnetic flux density 78located near portions of the lower stator 12, upper stator 46, magnet26, second armature 42 and coil 16 in accordance with the presentinvention. The top surface 60 of the magnet 26 is located adjacent thesecond armature 42 so that its magnetic field is added to the firstmagnetic field 10 generated by the coil 16 to thus form the secondmagnetic flux density 78. The flux density vectors are oriented in asubstantially counterclockwise configuration in the magnet 26, secondarmature 42, and gap 36. Further, the magnetic flux density vectors areconcentrated at the tip surface 64. This serves to increase the force onthe second armature 42. In addition, the magnetic flux density in theupper section 22 of the lower stator 12 is approximately 2524 kGauss,resulting in an increased flux density in the upper section 22 over thatof conventional solenoids. It is noted that the shape of the lowerstator 12, size of the gap 36 and other associated parameters may beoptimized for use with the magnet 26.

[0019] Referring to FIG. 4, first 80 and second 82 curves depictingforce and displacement properties for a conventional solenoid and forthe solenoid 24, respectively, are shown. In particular, it can be seenthat armature force for a given armature displacement is substantiallyincreased for the solenoid 24 relative to that of a conventionalsolenoid. This results in substantially improved valve performance.

[0020] While the invention has been described in conjunction withspecific embodiments, it is evident that many alternatives,modifications, permutations and variations will become apparent to thoseskilled in the art in light of the foregoing description. Accordingly,it is intended that the present invention embrace all such alternatives,modifications and variations as fall within the scope of the appendedclaims.

What is claimed is:
 1. A solenoid, comprising: a housing having a coilfor generating a first magnetic field; an armature slidably mounted insaid housing; a permanent magnet having a second magnetic field, whereinsaid magnet is located adjacent said armature; and a stator affixed insaid housing for cooperation with said armature and said magnet to forma third magnetic field.
 2. The solenoid according to claim 1, whereinsaid stator has a frusto-conical configuration.
 3. The solenoidaccording to claim 1, wherein a magnetic flux density of said thirdmagnetic field has a counterclockwise orientation.
 4. The solenoidaccording to claim 2, wherein a magnetic flux density of said thirdmagnetic field is concentrated on a tip of said stator.
 5. The solenoidaccording to claim 4, wherein a magnetic flux density in an upperportion of said stator is approximately 2524 kiloGauss.
 6. The solenoidaccording to claim 2, wherein said magnet is colinear with a tip of saidstator.
 7. A valve, comprising: a housing having first and second portsand a coil for generating a first magnetic field; an armature slidablymounted in said housing, said armature having a valve head for closingand opening said first port; a permanent magnet having a second magneticfield, wherein said magnet is located adjacent said armature; a statoraffixed in said housing for cooperation with said armature and saidmagnet to form a third magnetic field.
 8. The solenoid according toclaim 7, wherein said stator has a frusto-conical configuration.
 9. Thesolenoid according to claim 7, wherein a magnetic flux density of saidthird magnetic field has a counterclockwise orientation.
 10. Thesolenoid according to claim 8, wherein a magnetic flux density of saidthird magnetic field is concentrated on a tip of said stator.
 11. Thesolenoid according to claim 8, wherein a magnetic flux density in anupper portion of said stator is approximately 2524 kiloGauss.
 12. Thesolenoid according to claim 8, wherein said magnet is colinear with atip of said stator.
 13. A method for operating a valve, comprising thesteps of: providing a housing having first and second ports; generatinga first magnetic field by using a coil; providing an armature having avalve head for closing and opening said first port; providing apermanent magnet for generating a second magnetic field, wherein saidmagnet is located adjacent said armature; and providing a stator forcooperation with said armature and said magnet to form a third magneticfield for moving said armature and thus said valve head to open andclose said first port.
 14. The method according to claim 13, whereinsaid stator has a frusto-conical configuration.
 15. The method accordingto claim 13, wherein a magnetic flux density of said third magneticfield has a counterclockwise orientation.
 16. The method according toclaim 14, wherein a magnetic flux density of said third magnetic fieldis concentrated on a tip of said stator.
 17. The method according toclaim 14, wherein a magnetic flux density in an upper portion of saidstator is approximately 2524 kiloGauss.
 18. The method according toclaim 14, wherein said magnet is colinear with a tip of said stator.